The most recent space-borne topography dataset launched in 2000. A decade later, German scientists are 
using orbital teamwork for amazing results.
The TerraSAR-X launched back in 2007, and is able to map the Earth’s surface to an accuracy of about 10 meters, which is impressive enough. But today, the same German team launched the TanDEM-X, an identical satellite, to work, well, in tandem with the TerraSAR-X for even better accuracy–down to only two meters.
The TanDEM-X will fly in a tight helix pattern around the TerraSAR-X, at an altitude of about 320 miles above the Earth. Both satellites map the Earth by bouncing microwaves off the surface and measuring the length of time it takes for them to return. The use of microwaves allows better topographical accuracy than using photographs, since microwaves can move right through obstacles that render the land invisible to sight. The eruption of the Icelandic volcano Eyjafjallajokull, for example, blanketed the surrounding area in thick black soot–but the satellites’ microwaves can zoom right past that. You can see that image pictured above.
The other major benefit of this system is that the map of the entire globe will be derived from one dataset, rather than patched together from scattered other bits of data. It’ll be more cohesive and consistent as a result.
So what’s the benefit of two satellites, rather than one?
The compact orbital dance will give the pair “stereo vision”, by enabling them to operate an interferometric mode in which one spacecraft acts as a transmitter/receiver and the other as a second receiver.
There are immeasurable benefits to having an accurate 3D rendering of the Earth’s surface. Military, research, scientific, environmental, humanitarian, civil, and commercial applications all spring to mind, from mapping low-altitude flight paths to mapping the spread of the Gulf oil spill.
The tandem satellites will take about three years to map the entire globe.
